141 Linked List Cycle.js

// Leetcode #141
// Language: Javascript
// Problem: https://leetcode.com/problems/linked-list-cycle/
// Author: Chihung Yu
/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

/**
 * @param {ListNode} head
 * @return {boolean}
 */
var hasCycle = function(head) {
    if(head === null || head.next === null){
        return false;
    }
    
    var faster = head.next;
    var slower = head;
    
    while(faster && slower){
        if(faster.val === slower.val){
            return true;
        }
        faster = faster.next;
        
        if(faster === null){
            return false;
        } else {
            faster = faster.next;
        }
        
        slower = slower.next;
    }
    
    return false;
};